The invention relates to a fuel injection pump and a method of controlling an amount of fuel injected by a fuel injection pump for internal combustion engines. As it is known, the majority of diesel engines have unpleasantly harsh combustion noises during idling or in the range of low partial loads. It is possible to reduce these noises by extending the time of injection in the range of respective rotational speeds. It is known to provide to this end in the case of fuel injection pumps, a bypass which opens into a pump working space and can be adjusted by an electric valve. In particular, at low rotational speeds, part of the fuel delivered into the pump working space, can flow via this bypass into a suction chamber or into a fuel tank, bypassing the fuel injection nozzles. In this manner, it is possible to extend the injection time. Here, the amount of injected fuel is a net difference between the quantity of fuel delivered from the pump working space, and the amount of fuel flowing via the bypass.
In a fuel injection pump of this kind, which is known from German Offenlegungsschrift No. 3,507,853, an electric valve is used which, in the de-energized condition, holds the bypass completely open and which closes the bypass as the electrical excitation increases. In a first operating condition, the valve for determining the injection phase is completely closed and in a second operating condition, during idling, the valve is only partially closed over the entire duration of injection, and thereby successfully reduces the fuel injection rate. To compensate for this, the duration of the partially closed condition must, in this operating range, be correspondingly extended compared with injection at a high injection rate in order to inject the same amount of fuel. In this fuel injection pump, the start of delivery and the end of delivery are determined solely by the closing and opening movement of the valve. This requires an exact coordination between the delivery movement of the pump plunger and the electrical control of the valve. Even slight irregularities in the coordination of these movements can result in major changes in the amount of fuel reaching the injection valves and, hence, in irregularities in fuel metering of the internal combustion engine.